Which app or website tells us what price can we pay for a car ?

I'm new to cars and wanted to buy a car.
I will be paying full cash, no financing.
If I go to a dealer and ask them to show they would show some cars and give us a price.
How to negotiate a good deal with the car sales rep ?
Is their a website or a smart phone app which I can use and then feed in
the make and model with options and it can show me what would be the best price to pay ?
This way I know I haven't paid too much for a car and got ripped off during
the car buying process
Thanks in advance
I will be paying full cash, no financing.
If I go to a dealer and ask them to show they would show some cars and give us a price.
How to negotiate a good deal with the car sales rep ?
Is their a website or a smart phone app which I can use and then feed in
the make and model with options and it can show me what would be the best price to pay ?
This way I know I haven't paid too much for a car and got ripped off during
the car buying process
Thanks in advance
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